1. Field of the Invention
This present invention relates to the fabrication methods used to produce semiconductor devices, and more specifically to methods used for planarizing devices using spin on glass, (SOG), chemical mechanical polishing, (CMP), and hot deposition of aluminum alloy metallization.
2. Description of Prior Art
A major objective of the semiconductor industry has been to continually improve device performance while still maintaining, or decreasing, the manufacturing cost of the specific semiconductor chip. This objective has been, in part, realized by the trend to micro-miniaturazation. The ability to fabricate semiconductor devices with sub-micron features, has allowed both the performance and cost objectives to be met. Smaller features positively influence performance by decreasing parasitic capacitances, as well as decreasing specific performance degrading resistances. In addition micro-miniaturazation has resulted in a decrease in chip size, thus enabling more chips to be placed on a specific size, starting silicon substrate, thus reducing the processing cost for a specific chip.
Micro-miniaturization has been accomplished by advances in several key semiconductor fabrication disciplines such as photolithography and reactive ion etching, (RIE). For example more sophisticated exposure cameras, as well as the development of more sensitive photoresist materials, have allowed sub-micron images to be routinely created in photoresist materials. In addition similar advances in anisotropic, dry etching processes, have allowed the sub-micron images in photoresist to be successfully transferred to underlying semiconductor materials. However smaller features, such as narrower metal interconnect lines, along with smaller spaces between interconnect lines, can result in difficulties in obtaining planar surfaces, which are needed to create successful subsequent upper level wiring lines. In addition to maintain the desired conductivity of the narrower metal lines, the height of the metal line has to be increased. This results in a higher aspect ratio than for counterparts fabricated with wider, thinner metal lines, again adding to the difficulties in filling the narrow spaces with insulator.
One method used by the semiconductor industry to fill narrow spaces, between metal lines, is a spin on glass, (SOG), process. Unlike more conventional insulator deposition processes, such as low pressure chemical vapor deposition, (LPCVD), or plasma enhanced chemical vapor deposition, (PECVD), where conformal coverage of the metal line with the deposited insulator still leaves a severe topography for subsequent wiring processes, the SOG process fills these narrow spaces, and after applying subsequent planarazation techniques, results a planar topography. Prior art has shown SOG applications, such as Kim, et al, in U.S. Pat. No. 5,354,713, as well as Fisher, et al, in U.S. Pat. No. 4,917,759. However these applications, although resulting in the desired planarity, also result in the SOG layer being exposed during subsequent metal depositions. The characteristics of the SOG layer include outgassing of incorporated oxygen or moisture during a hot metal deposition process. This outgassing can result in degraded aluminum metal properties, such as increased resistivity, due to the reaction with the SOG outgassing components.
This invention will describe a process for achieving planar topographies, using a SOG process to fill narrow spaces between metal lines. However this invention will show SOG planarization processes, and encapsulation techniques, used to prevent SOG outgassing during subsequent hot aluminum depositions.